The present invention concerns a process and furnace for burning refuse.
Various types of furnaces--parallel-flow, inverse-flow, and mid-flow--are described and discussed by D. O. Reimann in "Verfahrenstechnik der Mullverbrennung", Die Industriefeurung, Essen, Vulkan-Verlag Dr. W. Classen, 1986, 23-32. Two parallel-flow furnaces are illustrated using schematic drawings. The top of each is in the form of a roof. The inside of the furnace communicates with a flue by way of the grate's burn-out section and its adjacent residue-precipitation shaft. The bottom of the furnace, namely the secondary combustion section, is in one parallel-flow furnace a sloping flue, and the residue-precipitation end roof of the jacket constitutes the floor. The top of the sloping flue communicates with an upright flue, and the flue gas is extensively diverted, especially at the lower edge of the residue-precipitation end roof. The whole flue in the other parallel-flow furnace is upright, although a definite but less extensive diversion is shown at the transition between the inside of the furnace and the flue.
The article devotes considerable attention to the stream of cold flue gas, which flows from the front of the grate, in the vicinity of the charging shaft. It is evident from the drawings that compare the different furnaces that, in a parallel-flow furnace, the cold gas flows to a considerable extent through the hottest part of the combustion section.
When refuse is incinerated in a grated furnace, it is loaded through a refuse-charging shaft and initially dried and heated at the front of the grate. The water evaporates and the burnable components turn into gas. Pyrolysis also occurs in this area, where the temperatures range up to 500.degree. C., It is accordingly of decisive importance, in order to minimize the level of pollutants in the exhaust leaving such a grated furnace on the whole, for the gases and particulate solids that convert into flue gas in the grate's drying and pilot section to be powerfully, turbulently, and intimately combined with the higher-temperature exhaust leaving the grate's actual combustion section. Assuming enough oxygen, both the temperature and turbulence of the flow field and the length of time spent in the vicinity of high temperature and turbulence are of decisive significance to how effectively the organic components are annihilated.
European Patent 0 579 987 A1 describes a rotating-cylinder incinerator with at least two primary-air nozzles aimed toward one another and toward a bed of fuel, generating two opposing vortices inside the cylinder. These vortices rotate around axes paralleling the axis of the cylinder and support the thermally induced motion of the burning gases. A secondary combustion section accommodates auxiliary burners or combined-air nozzles oriented to augment the opposing vortices leaving the cylinder.